LISBON — During President Reagan's 10-day European trip, which ends today when he arrives back at Andrews Air Force Base outside Washington, he has followed an exhausting schedule crammed with formal dinners, official lunches and work sessions. He has made numerous speeches and toasts and frequent off-the-cuff remarks to officials and reporters covering the trip.

And, through it all, the 74-year-old President has seldom seemed to tire and has rejected any suggestion that he might be tired. But the same could not be said for some reporters and members of his staff, who have complained of being exhausted.

When a reporter covering Reagan's session with Portuguese Prime Minister Mario Soares asked the President if he wasn't exhausted, Reagan, dismissing the question with a wave of the hand, said, "Youth is on my side."

Later, Reagan, referring to the press, told Soares, "Why don't I tell them to take the rest of the day off."

In a television interview, White House Chief of Staff Donald T. Regan jokingly suggested that some members of the press "were tired before they started."

"But as far as the President is concerned," he said, "I can tell you this. He has remarkable resilience. He bounces back, goes to bed tired, comes up in the morning and he's fresh and ready to go. It's been a remarkable performance on his part. He's tiring me out, frankly."

And Secretary of State George P. Shultz, in his final press briefing in Lisbon, described it as "a very hard working trip" and said, "I'm a little on the tired side now."

The Reagan Administration has long been discouraging use of the expression "Star Wars" to describe the President's research program for a space-based defense system against nuclear missiles. The approved term is Strategic Defense Initiative.

When Ed Schumacher, the Madrid bureau chief of the New York Times, asked Shultz a question about the program here Thursday, the exchange started this way:

Schumacher: Mr. Secretary, the President said in Strasbourg that while we're developing 'Star Wars,' we would remain within the. . . .

Shultz: I doubt that he used that word.

Schumacher: Well, I. . . .

Shultz: Strategic Defense Initiative is the word you're looking for.

A good deal of laughter followed, then Schumacher said, "I'm just a poor foreign correspondent, not one of the sophisticated Washington guys."

The malfunctioning TelePrompTer that momentarily embarrassed President Reagan on Wednesday and fouled up the beginning of his speech to the European Parliament at Strasbourg, France, has left an indelible impression on the presidential staff.

Chief of Staff Regan, answering a television reporter's question in Lisbon on Thursday about whether there would be changes in the tax simplification plan he drafted when he was Treasury secretary, said, "It was written on a TelePrompTer--excuse me--it was written on a word processor. I think I've got TelePrompTer on my mind after Strasbourg. But since it is on a word processor, we recognized it was going to be changed."

Connie Romero figures she has traveled over a million miles while working for five Presidents during 22 years as a White House press secretary. But never, Romero said, has she faced an experience quite as horrifying as she did during one night of President's Reagan's current trip.

Romero, like half the White House staff and press corps, was housed aboard a cruise ship docked on the Rhine River while Reagan was in Bonn for last week's economic summit--"the boat people," they were called.

Feeling ill and unable to sleep in her tiny cabin, she got up in the middle of the night and pulled back the curtain covering two portholes just above the water line. She though she would watch the river barges go by.

But what Romero saw "scared the bejeezers out of me," she said. "I thought it was somebody going to attack me. It looked so weird, like some sort of monster. I screamed like hell and was close to crying."

When the "monster" screamed back, Romero realized she was looking at herself in hair curlers, her tired eyes reddened by an overnight flight from Washington. It was a reflection in a porthole-shaped mirror.

"I was still shaking an hour later," she recalled in Lisbon. "And I still haven't got caught up on all the sleep I lost that night."

Many Europeans protesting the Reagan visit are doing so as an indirect way of attacking political leaders, like Prime Minister Mario Soares of Portugal, who invited the President. One Portuguese protester made this obvious. His spray-painted graffiti in downtown Lisbon proclaimed, in English, "Reagan, Go Home," and then added, in Portuguese, "Take Soares With You."

Old Lisbon was splattered with anti-Reagan posters and graffiti. Some protesters had even spray-painted the sides of several old buildings with the slogan, in English, "Nancy Reagan, Go Home." These were on a narrow, antique street that winds through the Alfama section of Lisbon to the top of the hill where St. George Castle offers a magnificent view of the city.

The First Lady did not see the graffiti. She was scheduled to visit St. George Castle during the stay in Lisbon, but the schedule was revised at the last minute, and the St. George castle stop was dropped.

Notebook contributors were Jack Nelson, George Skelton and Stanley Meisler.